Try Mike Brooks. He's on this forum and builds an outstanding product. I'd suggest a full jug choked 12 gauge fowler, if only because that's what I'm familar with. I've been shooting a flint fowler less than a year and have harvested over 80 birds with it so far. Haven't gotten any turkeys with it, simply because I like wing shooting. It throws an awesome pattern out to forty yards, and is lethal well beyond that range.
There may be less expensive guns out there, but none better than Mike's. A cheaper gun is usually just a transitional piece to the one you want. It won't perform as well, and you won't recover your money when you want to trade out of it. If you buy a nice custom gun, you'll be satisfied right from the start, and if your interests change down the road, you'll not only get your money back, but probably pocket a few bucks as well.
Contact Mike and discuss your project with him. His components are top notch, and his workmanship is amazing.